German patent document DE 10 2007 041 528 A1 discusses a laser ignition device or laser spark plug for an internal combustion engine, including a laser-active solid body, a combustion chamber window and a casing, where the casing and the combustion chamber window are interconnected in a continuous material manner at least indirectly to seal off the interior chamber from the combustion chamber.
At one end of the casing facing the combustion chamber, there is a so-called combustion chamber window, which is able to transmit the laser beams generated in the ignition laser. This combustion chamber window must be accommodated in a casing of the ignition laser, so as to form a seal. There are strict requirements for the sealing between the combustion chamber window and the casing, since during operation of the internal combustion engine, surface temperatures of more than 600° C. may occur at the combustion chamber window. In addition, there are also intermittent compressive loads of up to 300 bar. When an ignition laser is used for the ignition of a gas turbine, low pressures do prevail in the combustion chamber of the gas turbine, but the surface of the combustion chamber window may reach temperatures of up to 1000° C.; instances of uncontrolled ignition by incandescence always having to be prevented.
It is clear that the interior of the ignition laser must be reliably sealed from the extremely high temperatures and pressures. If the exhaust gases should happen to reach the interior of the ignition laser, this would lead to failure of the ignition laser.